Diverse copolymers having different physical properties have been conventionally synthesized by copolymerizing a vinyl monomer alone or a mixture of various vinyl monomers. Among them, a method of copolymerizing a mixture including two or more kinds of vinyl monomers, or mixing heterogeneous copolymers have been generally used since a polymer using a vinyl monomer alone cannot meet various requirements for the physical property. However, in a case where a mixture of various vinyl monomers is simply copolymerized, the properties possessed by each monomer unit tend to be averaged.
In addition, with only simple mixing of two or more kinds of copolymers, the copolymers were not intermingled with each other, and the properties were often worse than the property possessed by each monomer unit.
To solve these problems, investigations have been performed for a copolymer using a macromonomer. A macromonomer is a high molecular weight monomer having a polymerizable functional group. A copolymer obtained by copolymerizing a macromonomer has a feature that each property of the macromonomer moiety and the monomer unit copolymerized with the macromonomer is not impaired and individual property can be expressed. Consequently, this kind of copolymer using macromonomer is suggested variously, for example, also in the field of an adhesive.
For example, Patent Document 1 discloses an adhesive composition containing a copolymer, which is obtained by copolymerizing a macromonomer having a number average molecular weight of 2000 g/mole to 50,000 g/mole and an ethyleny unsaturated monomer, and is dispersed in an aqueous medium having a specific solid content.
In addition, Patent Document 2 discloses a resin composition for an adhesive obtained by copolymerizing an alkyl(meth)acrylate monomer and a macromonomer having a number average molecular weight of 1,000 to 200,000 and a glass transition temperature of 30 to 150° C.